Although the demand for battery capacity on mobile devices has grown with the increase in high data rate applications, battery technology has not kept up with this demand. Therefore, the growth in energy demand coupled with global warming provide a new trend in wireless communication known as energy-efficient transmission. In this paper, the energy-efficient resource allocation for a two-hop uplink multiuser relay-based system is studied. We adopt the orthogonal frequency division multiplexing as the physical layer modulation technique. Assuming that the base station has all the channel state information, an energy efficiency optimization problem by joint subcarrier assignment, bit and power allocation is formulated. We first develop a near-optimal resource allocation scheme to maximize the overall energy efficiency; then, an efficient resource allocation algorithm is provided to solve the problem with relatively low computational complexity. Furthermore, fairness constraint among users is imposed on the system to guarantee each user's QoS. Our joint resource allocation algorithm is proved to achieve a considerable improvement in terms of energy-saving and simultaneously decreases outage probability by simulation results. Copyright © 2012 John Wiley & Sons, Ltd.